Trophic niche of North American Great Horned Owls

8 Pages·2002·3 MB·English

by  Lee A Cromrich

J RaptorRes. 36(1):58~65
© 2002 The Raptor Research Foundation, Inc.
TROPHIC NICHE OF NORTH AMERICAN GREAT HORNED OWLS
Lee a. Cromrich,^ Denver W. Holt, and Shawne M. Leasure
MT
Owl Research Institute, PO. Box 39, Charlo, 59824
—
Abstract. The trophic niche ofGreat Horned Owls {Bubo virginianus) was summarized using 22 North
American studies reporting >100 prey items each. Twenty-one of these studies were reviewed from the
published literature, and one, our Montana data, is presented here for the first time. More than 92
species from four taxonomic classes have been recorded from 19 2*78 prey items. Mammals constituted
>93.3% of prey from all studies, with six studies reporting 100% mammalian prey. Food-niche breadth
ranged from 2.09-19.15 {x = 5.1*7) for combined studies, 2.12-19.15 (x = 6.29) for breeding seasons,
and 2.09-4.72 (x = 3.50) for non-breeding seasons. Evenness values ranged from 0.408-0.840 (a =
0.620) for combined studies, 0.420-0.703 {x = 0.596) for breeding seasons, and 0.408-0.724 {x = 0.609)
for non-breeding seasons. Estimated masses of individual prey species ranged between 2 and 6300 g.
Birds were only a minor part of the owl diet, although a variety of species were eaten.
KeyWords: diet, food-niche breadth. Great Horned Owl; Bubo virginianus; North America.
Nicho trofico del Gran Buho Cornado Americano
—
Resumen. El nicho trofico de {Bubo virginianus) fue corapendiado usando 22 estudios norte americanos
reportando >100 Items presa cada uno. Veintiuno de esos estudios fueron revisados en la literatura
publicada, y uno, nuestros datos de Montana, se presentan aqui por primera vez. Mas de 92 especies
de cuatro clases taxonomicas han sido registradas a partir de 19 278 Items presa. Los mamiferos cons-
tituyeron >93.3% de presas en todos los estudios, con seis estudios reportando 100% de presas ma-
mlferas. La amplitud del nicho alimenticio estuvieron en el rango de 2.09-19.15 {x = 5.17) para estudios
combinados, 2.12-19.15 {x = 6.29) para estaciones reproductivas, y 2.09-4.72 (x = 3.50) para tempo-
radas no reproductivas. La masa estimada de especies presa individualmente estuvo entre 2 y 6300 gr.
Las aves fueron tan solo una parte menor de la dieta del buho, aunque una variedad de especies fueron
consumidas.
[Traduccion de Cesar Marquez]
The Great Horned Owl {Bubo virginianus) is per- sons between a few Neotropical and Nearctic lo-
haps the most widely-distributed owl in North calities, but compared owl diets from only two
America (Houston et al. 1998, Holt et al. 1999). regions in North America. Our paper summarizes
Numerous studies of the food habits of Great the trophic niche of Great Horned Owls from 22
Horned Owls have been conducted in North North American studies; 21 from published litera-
America and it has been considered to be an op- ture, and one, our original Montana data.
portunistic feeder. Indeed, the Great Horned Owl Our objectives were to: (1) determine Great
has been reported to have the broadest diet of any Horned Owl trophic niche from west-central Mon-
North American owl species (Marti and Kochert tana and (2) compare trophic niche among North
1996, Houston et al. 1998). However, the owl’s tro- American studies.
phic niche has not been reviewed continent-wide.
Methods
Earhart andJohnson (1970) summarized principal
food habits of Great Horned Owls from published In Montana, we collected pellets and prey remains an-
literature, but did not identify prey to the species nually from 10 territories in the Missoula and Mission
valleys during the breeding and non-breeding seasons
level, provide prey numbers, or discuss their con-
from 1987-95. Prey was identified using local dichoto-
clusions. Jaksic and Marti (1984) made compari- mous keys for mammals (Hoffmann and Pattie 1968) and
by comparing feather and body parts of prey with mu-
seum specimens at the Philip L. Wright Zoological Mu-
^ E-mail address: [email protected] seum (University ofMontana). Numbers and proportions
58
March 2002 Great Horned Owl Trophic Niche 59
ofprey types were then compared between breeding and Table 1. The number of individual prey consumed by
non-breeding seasons for Montana. Comparisons of tro- Great Horned Owls during breeding and non-breeding
phic niche were then made among other available North seasons in Montana from 1987-95.
American data sets.
We defined trophic niche as the relationship between
owls and their prey. We followed Marti’s (IQS'/) defini- No. OF Prey
tions for trophic diversity in which a broad food-niche
Breeding Non-Breeding
breadth (FNB) has a high number ofprey species, which
are nearly equally distributed, and a narrow food-niche Species Season Season
breadth has a low number of prey species unequally dis- Mammals
tributed. However, we found no method to determine
the statistical significance between narrow andwide food- Microtus pennsylvanicus 1264 902
niche breadth. We compared owl trophic niche from 22 Microtus montanus 1158 470
North American studies with >100 prey items each (Ta- Microtus spp. 72 159
bles 1-3). We then divided these studies into breeding Peromyscus maniculatus 37 52
season and non-breeding season diets. To compare tro- Thomomys talpoides 54 39
phic niche among studies, we primarily used prey iden-
Ondatra zibethicus 13 14
tified to the species. Prey identified to genus were in-
Mustelafrenata 1 —1
cluded if they occurred frequently or exhibited an
unusual body mass. Insects, arachnids, and unidentified Sylvilagus nuttallii —2
reptiles, birds, and mammals were eliminated from tro- Tamias amoenus —1
phic niche comparisons because they were either not Tamiasciurus hudsonicus —2
identified to genus or occurred only rarely (<1%) in the Glaucomys sabrinus 1
diet.
Birds
Food-niche breadth {H') was calculated for each study
using the antilog of the Shannon-Weiner diversity index Sturnus vulgaris 30 4
(Marti 1987). We used this equation because it is linearly Phasianus colchicus 12 4
related to the number of prey categories in the sample. Fulica ajnericana 6 1
Evenness was calculated using Alatalo’s (1981) mo~difi- Pica pica 7 —1
cation of Hill’s (1973) equation; Evenness = {N^ 1)/ Turdus migratorius 3
v{aNliue—s r1a),ngwehefrreom ze—roetxoponHe'. aAnndevenness valuEeveonfnoenses Colaptes aumtus 2 —1
Xanthocephalus xanthocephalus 12
indicates prey proportions in the diet are equal. We com-
pared food-niche breadth and evenness values from all Anas platyrhynchos 2 —2
studies as well as those from breeding and non-breeding Anas spp. 1 —
seasons using the Mann-Whitney Gtest (Eowler and Co- Bombycilia spp. 1 —
hen 1990). Sturnella neglecta 1 —
Spearman rank correlation (Fowler and Cohen 1990) Asia otus 1 —
was used to examine the relationship between the num- Porzana Carolina 1 —
ber ofmammalian species and number ofpreyitemswith
Rallus limicola 1 —
food-niche breadth values among studies. We did so to Bonasa umbellus —1
determine if wider food-niche breadth values were asso-
Agelaius phoeniceus 1
ciated with increased numbers of prey or species in the
diet. The Spearman rank correlation was also used to Other
—
examine the relationship between number of prey items
Catostomus spp. 4
and food-niche breadth because food-niche breadth val-
crayfish 6 —1
ues can fluctuate with sample size, thus influencing the
squawfish 2
results.
A relative-size category of the main prey classes eaten Total 2696 1654 = 4350
by the owls was derived using body mass estimates of
mammals (Whitaker 1992) and birds (Dunning 1984).
Standard mean prey biomass estimates were not calculat-
non-breeding season. Although collectively the
ed based on species because of unfounding factors. For
example, standard prey biomass estimates are usually de- owls ate a wide variety of prey {N = 28), they ate
rived from the adult age class and do not consider other predominately small mammals, particularly voles
age classes in the population. Further, mean prey biomass (Table 1).
estimates generally give whole carcass masses and do not During the breeding season, the owls consumed
consider that only specific portions of some medium to
28 species of prey. Of these however, they ate pre-
large prey are eaten (Holt 1993, 1994).
dominately small mammals, especially Microtus
Results voles (92.5%, N = 2494). During the non-breeding
The Montana study yielded 4350 prey items: season, the owls ate only 16 species of prey, again
N
2696 from the breeding season and 1654 from the consuming predominately Microtus\o\e^ (92.5%,
60 Cromrich et al. VoL. 36, No. 1
Table 2. Landscape diets of Great Horned Owls in North America. Percent ofprey in taxonomic classes calculated
from 22 studies, representing 19 278 prey items.
Percent
No. OF Prey Osteichthyes Crustacea Aves Mammalia Location Source
Breeding season
MT
2696 0—.2 0—.2 3—.09 6.6 This study
1896 — — 100.0 OR Maser 8c Brodie 1966
1300 1.4 98.6 ID Marti & Kochert 1996
—
398 1—.5 2.8 95.7 UT Smith & Murphy 1973
356 0.8 — 2.2 96.9 WY Craighead & Craighead 1969
276 3—.3 — 31—.5 65.2 NY, NJ, CT Bosakowski & Smith 1992
MB
209 100.0 Bird 1929
—
142 — 9—.2 20.4 70.3 MI Craighead Sc Craighead 1969
OH &
119 30.3 69.7 Springer Kirkley 1978
Non-breeding season
— —
1845 1.4 98.6 MI Craighead 8c Craighead 1969
—
MT
1654 0—.1 1.0 98.9 This study
MT
756 2—.5 — 1.9 95.6 Seidensticker 1968
584 — — 0.3 99.7 GA Rudolph 1978
210 — — 2—.4 97.6 IN Kirkpatrick 8c Conway 1947
161 — — — 100.0 NE Rickart 1972
122 100.0 YT Weir & Hanson 1989
Breeding and non-breeding seasons
2571 —- 0—.1 4.4 95.2 WI Errington 1932
CO
2152 — 1.7 98.1 Marti 1974
809 0—.1 — 1—.7 98.1 WA Knight &Jackman 1984
568 100.0 CA Barrows 1989
—
273 — 0—.7 21—.2 78.0 WI Orians 8c Kuhlman 1956
178 100.0 OK Tyler &Jensen 1981
^ 1531). The decreased prey species diversity dur- species overall, Microtus {N — 10 studies), Peromys-
ing the non-breeding season reflected the fewer cus (N — 6), Perognathus {N = 2), Sigmodon (N —
=
species of prey available during the fall and winter 1), and Lepus (N 1) species represented the
months in Montana. highest percentage of prey in all studies. Overall,
The 22 studies combined yielded 19 278 prey food-niche breadth values ranged from 2.09-19.15
items (Table 2) from eightwestern, six central, and (x = 5.17, SD ± 3.61) (Table 3). Food-niche
=
three eastern states, and two Canadian provinces. breadth values for the breeding season (range
Studies from New York and Pennsylvania (Latham 2.12-19.15, X - 6.29, SD ± 5.39, N = 9) and non-
= SD
1950), and Alberta (Rusch et al. 1972, Mclnvaille breeding season (range 2.09-4.72, x 3.50,
and Keith 1974, Adamcik et al. 1978) were also re- ± 0.82, N = 7) were similar. Food-niche breadths
U
viewed but omitted from trophic calculations be- were not significantly different (Mann-Whitney
cause dominant prey species were not always iden- = 24.5, P > 0.05) between seasons.
tified to genus or species. The broadest food-niche breadth (FNB — 19.15)
The owls consumed >92 prey species from four was from New York, NewJersey, and Connecticut,
taxonomic classes: Osteichthyes, Crustacea, Aves, where 15 mammal species constituted 65.2% of the
and Mammalia (Table 2). Mammals composed diet, with Peromyscus representing 14.3% (Bosa-
^65.2% of the prey from each study, constituting kowski and Smith 1992) (Table 3). Fourteen other
93.3% of the total prey from all studies. Six studies mammal, 20 bird, and two fish species comprised
reported 100% mammalian prey (Table 2). the remainder. The broad FNB in this study, com-
Although the owls preyed on a broad number of pared to other studies, may be explained by the
March 2002 Great Horned Owl Trophic Niche 61
Table 3. Trophic parameters calculated from twenty-two studies representing 19 278 prey items.
Food-niche
No. OF Prey Breadth Evenness Location Source
Breeding season
MT
2696 3.27 0.644 This study
OR
1896 2.12 0.465 Maser &c Brodie 1966
1300 8.12 0.686 ID Marti & Kochert 1996
398 4.47 0.420 UT Smith & Murphy 1973
WY &
356 2.85 0.566 Craighead Craighead 1969
276 19.15 0.670 NY, NJ, CT Bosakowski & Smith 1992
MB
209 2.94 0.687 Bird 1929
142 4.55 0.527 MI Craighead & Craighead 1969
OH &
119 9.10 0.703 Springer Kirkley 1978
Non-breeding season
1845 2.94 0.669 MI Craighead &: Craighead 1969
MT
1654 3.43 0.649 This study
MT
756 3.91 0.622 Seidensticker 1968
584 2.09 0.724 CA Rudolph 1978
210 4.72 0.631 IN Kirkpatrick & Conway 1947
NE
161 3.84 0.558 Rickart 1972
122 3.56 0.408 YT Weir & Hanson 1989
Breeding and non-breeding season
2571 4.89 0.629 WI Errington 1932
CO
2152 6.36 0.605 Marti 1974
WA
809 5.27 0.602 Knight &:Jackman 1984
568 3.89 0.840 CA Barrows 1989
273 6.98 0.604 WI Orians & Kuhlman 1956
178 5.87 0.720 OK Tyler &Jensen 1981
large number of bird, as well as mammal, species cantly different (Mann-Whitney U = 30, P > 0.05)
included in the diet, or the relatively small sample between seasons.
size (N= 276). A weak positive correlation existed between the
Food-niche breadth calculated from Ohio number of mammalian species in the diet and
(Springer and Kirkley 1978) was also broad (9.10) food-niche breadth values (r^ = 0.299, P < 0.01).
compared to other studies (Table 3). In this study, A weak negative relationship occurred between the
six mammal species constituted 69.7% of the owl’s number of prey items and food-niche breadth val-
mammal
diet with Microtus representing 26.1%. Six = P >
ues (r, —0.207, 0.01), suggesting that sam-
and 12 bird species represented the remainder of
ple sizes were not influencing the results.
ntihae d(i2e.t0.9)T,heOrneagrornowe(s2t.12F)N,BWsycoammiengfro(2m.8C5a)liafonrd- Mammal prey biomass ranged from 2 g, (masked
shrew {Sorex cinereus^) to 6300 (striped skunk [Me-
Manitoba (2.94), respectively (Table 3). In all these g,
cases, small mammals dominated the diet (Bird phitis mephitis}) (Whitaker 1992). The m^orityofprey
1929, Maser and Brodie 1966, Craighead and ranged from 2-1800 g and included shrews, voles,
Craighead 1969, Rudolph 1978). mice, rats, pocket gophers, squirrels, and rabbits. The
Evenness values overall ranged from 0.408—0.840 dominant prey from each study, Microtus, Peromyscus,
(x = 0.620, SD ± 0.101). Evenness values for the Perognathus, Sigmodon, and Lepusranged in body mass
breeding (range — 0.420-0.703, x = 0.596, SD ± from 16-85 g, 10-43 g, 16-47 g, 80-120 g, and 1800-
0.105, N ~ 9) and non-breeding season (range — 3600 g, respectively (Whitaker 1992). Other medium-
0.408-0.724, A = 0.609, SD ± 0.102, N = 7) were sized mammals, including yellow-bellied marmot
also similar (Table 3). Evenness was not signifi- {Marmotaflaviventris) and white-tailedjackrabbit {Le-
. , .
62 Cromrich et al. VoL. 36, No. 1
pus toimsendii) rarely occurred in the diet and ranged {Glaucidium brasilianum) (Proudfoot 1997) and
from 2200-4500 Northern Pygmy-Owl {Glaucidium gnoma) (Holt
g.
Birds were not a major part of the owl’s diet, but and Leroux 1996, Holt and Petersen 2000). More
a wide variety of species were eaten. Waterfowl, specialized species include the Snowy Owl {Nyctea
shorebirds, pheasants and allies, and passerines scandiaca) (Watson 1957, Parmelee 1992), Short-
represented the majority of bird prey. Several owl eared Owl {Asio flammeaus) (Holt 1993, Holt and
species were also reported as prey in nine studies: Leasure 1993), Northern Saw-whet Owl (Holt et al.
Northern Saw-whet Owl (Aegolius acadicus) (Bosa- 1991, Cannings 1993), and Barn Owl (Marti 1989,
kowski and Smith 1992), Long-eared Owl {Asio 1992).
otus) (Marti 1976, Holt this study), Barn Owl {Tyto Other Bubo species have a trophic niche similar
alba) (Knight and Jackman 1984), and Eastern to the Great Horned Owl. Herrera and Hiraldo
Screech-Owl {Otus asio) (Errington 1932, Orians (1976) reported FNB values ranging from 2.40-
and Kuhlman 1956, Craighead and Craighead 6.68 (x = 4.13, SD ± 0.01) for the Eurasian Eagle-
1969, Bosakowski and Smith 1992). Body masses of Owl {Bubo bubo) in Europe.Jaksic and Marti (1984)
avian prey ranged from: 318-1100 waterfowl; 74- found that Great Horned Owls and Eurasian Eagle-
g,
415 g, shorebirds; 178-1317 g, pheasants and allies; Owls followed a similar trophic pattern in North
88-580 g, owls; and 29-458 g, passerines (Dunning American and European shrubland. Donazar et al.
1984). Passerines constituted most of the avian (1989), however, reported limited dietary conver-
prey. gence between these two species. They attributed
discrepancies in trophic diversity to the differences
Discussion
between similar North American and European bi-
Great Horned Owls are generally considered to omes, variations in the composition and abun-
be opportunistic feeders, preying on a broader dance of prey types, and differences in tbe body
range of species than any other North American masses of Great Horned Owls and Eurasian Eagle-
owl (Craighead and Craighead 1969, Voous 1988, Owls.
Marti and Kochert 1996, Houston et al. 1998). Bo- The moderate trophic niche of Great Horned
sakowski and Smith (1992) reported such unusual Owls could be the result of several factors, includ-
species as a raccoon {Procyon lotor), opossum {Di- ing prey species size, diversity, density, availability,
delphis virginiana) and a Red-shouldered Hawk and distribution. Marti (1974) suggested that al-
{Buteo lineatus); Marti (1974) reported a yellow-bel- though owls can capture a broad range of prey siz-
lied marmot and black-tailed prairie dog {Cynomys es, an optimum size exists in terms ofhow efficient-
ludovicianus); Errington (1932) reported a striped ly a particular individual prey item can be found
skunk; and Rudolph (1978) reported a Brazilian and caught. He argued that very small prey is only
free-tailed bat {Tadarida brasiliensis) Llinas-Gutier- efficient for Great Horned Owls ifit can be caught
rez et al. (1991) reported a wide variety of arach- quickly and easily. Marti felt that prey density, ease
nids, insects, and reptiles in the owl diet, and Roh- of killing, overlap of time of activity between pred-
ner and Doyle (1992) reported a Great Horned ator and prey, and learning by individual owls all
Owl feeding on an adult Northern Goshawk {Ac- determine what proportions ofthe diet a particular
cipiter gentilis) prey species will comprise.
The moderate trophic niche (high number of The Great Horned Owl’s moderate food-niche
prey species unequally distributed [see Methods breadth may also reflect the habitat or time of day
section] of the Great Horned Owl reported here- in which they forage. Open areas the Great
)
in somewhat contrasts with previous studies (see Horned Owl inhabits are frequented by mice,
text). Excluding predominately insectivorous owl voles, lagomorphs, and gophers, which may
species, the Great Horned Owl’s moderate food- emerge during the owl’s optimal feeding periods
niche breadth (opportunistic feeding) aligns it of evening, night, and early morning (Maser et al.
with species such as the Burrowing Owl {Speotyto 1970) The community structure of predators with-
.
cunicularia) (Haug et al. 1993), Spotted Owl (Strix in a particular habitat may also affect food-niche
occidentalis) (Gutierrez et al. 1995), and Eastern breadth. Marti et al. (1993) found that although
Screech-Owl (Gehlbach 1995), for example. Spe- predators in an area may utilize prey resources in
cies apparently more opportunistic than Great different fashions, patterns of resource use do
Horned Owls include the Ferruginous Pygmy-Owl emerge, particularly in terms of predator size.
.
March 2002 Great Horned Owl Trophic Niche 63
The diet of Great Horned Owls may vary de- Owls during a snowshoe hare cycle. Can. Field-Nat. 92
pending upon the particular region the owls in- 156-166.
habit (Marti et al. 1993). Hayward et al. (1993) Aiatalo, R.V. 1981. Problems in the measurement of
found that coastal Great Horned Owls in Washing- evenness in ecology. Oikos 37:199-204.
ton fed exclusively on birds during the summer Barrows, C.W. 1989. Diets of five species of desert owls
West. Birds 20:1-10.
months. Bosakowski et al. (1989) reported owls liv- Bird, R.D. 1929. The Great Horned Owl in Manitoba.
ing in the deciduous forests of New Jersey, New
Can. Field'Nat. 43:79-83.
York, and Connecticut preyed more heavily upon Bosakowski, T, R. Speiser, and D.G. Smith. 1989. Nest-
birds than those living in open coniferous forests ing ecology of forest-dwelling Great Horned Owls,
of the western United States. Desert owls fed on a Bubo virginianus, in the eastern deciduous forest bi-
variety of arachnids, insects, and reptiles because ome. Can. Field-Nat. 103:65-69.
of their availability and abundance in that biome AND D.G. Smith. 1992. Comparative diets of sym-
(Jaksic and Marti 1984, Barrows 1989, Llinas-Gu- patric nesting raptors in the eastern deciduous forest
biome. Can.]. Zool. 70:984—992.
tierrez et al. 1991).
Cannings, RJ. 1993. Northern Saw-whet Owl (Aegohus
Jaksic and Marti (1984) found that the diversity
acadicus). In A. Poole and F. Gill [Eds.], The birds of
of Great Horned Owl prey at the class level was
North America, No. 42. The Academy of Natural Sci-
very low in the temperate regions and very high in ences, Philadelphia, PA and The American Ornithol-
the desert regions of North America. They be- ogists’ Union, Washington, DC U.S.A.
lieved this difference reflected the greater repre- Craighead, JJ- AND F.C. Craighead. 1969. Hawks, owls
sentation of mammals in the diet of temperate and wildlife. Dover Publications, NewYork, NYU.S A.
owls, thus resulting in a moderate trophic niche. Donazar, J.A., F. Hiraldo, M. Delibes, and R.R. Estrel-
Great Horned Owls may respond opportunisti- la. 1989. Comparative food habits of the Eagle Owl
cally to the local profile of prey sizes and densities Bubo bubo and the Great Horned Owl Bubo virginianus
(Jaksic and Delibes 1987, Jaksic 1988). Llina- in six Palearctic and Nearctic biomes. Ornis Scand. 20:
298-306.
Gutierrez et al. (1991) suggested that lagomorphs
Dunning,J.B. 1984. Bodyweights of686 species ofNorth
and rodents were the dominant prey species in
American birds. West. Bird Band. Assoc. Mono. No. 1
their study compared with other desert studies in Earhart, C.M. and N.K. Johnson, 1970. Size dimor-
the region because oftheir high abundance. Rusch phism and food habits of North American owls. Con-
et al. (1972) reported that the diet of Great dor 72:251-264.
Horned Owls was strongly affected by changes in Errington, P.L. 1932. Food habits ofsouthern Wisconsin
the numbers of snowshoe hare {Lepus americanus) raptors. Condor 34:176-186.
They found that in years with high snowshoe hare Fowler, J. and L. Cohen. 1990. Practical statistics for
populations, owls exhibited higher predation rates held biology. Great Britain Redwood Press Limited,
Manchester, U.K.
on snowshoe hare and lower predation rates on
Gehlbach, F.R. 1995. Eastern Screech-Owl {Otus asio) In
mice and voles.
A. Poole and F. Gill [Eds.], The birds ofNorth Amer-
The data herein support the general conclusion
ica, No. 165. The Academy of Natural Sciences, Phil-
that Great Horned Owls prey on a wide range of adelphia, PA and The American Ornithologists’
species. However, the data also show convincingly Union, Washington, DC U.S.A.
that Great Horned Owls feed primarily on only Gutierrez, A.B. Franklin, and W.S. Lahave. 1995
R.J.,
three to four species ofvoles and mice under most Spotted Owl {Strix occidentalis) In A. Poole and F. Gill
.
conditions, indicating a moderate food-niche [Eds.], The birds of North America, No. 179. The
breadth. Academy of Natural Sciences, Philadelphia, PA and
The American Ornithologists’ Union, Washington,
Acknowledgments DC
U.S.A.
We thank the Flathead Indian Reservation, Montana Haug, E.A., B.A. Millsap, and M.S. Martell. 1993. Bur-
Department of Fish, Wildlife and Parks, United States rowing Owl (Speotyto cunicularia) In A. Poole and E
.
Fish and Wildlife Service, and many private landowners Gill [Eds.], The birds of North America, No. 61. The
for access to lands. Marc Bechard, Carl Marti, and Fabian Academy of Natural Sciences, Philadelphia, PA and
Jaksic made thoughtful comments on the manuscript. The American Ornithologists’ Union, Washington,
DC
U.S.A.
Literature Cited
Hayward,J.L.,J.G. Galusha, and G. Frias. 1993. Analysis
Adamcik, R.S., A.W. Todd, and L.B. Keith. 1978. De- of Great Horned Owl pellets with Rhinoceros Auklet
mographicand dietary responses of Great Horned remains. Auk 110:133-135.
64 Cromrich et al. VoL. 36, No. 1
Herrera, C.M. and F. Hiraldo. 1976. Food-niche and northeastern United States. Pennsylvania Game Gom-
trophic relationships among European owls. Ornis mission, Harrisburg, PA U.S.A.
Scand. 7:29-41. Llinas-Gutierrez, G. Arnaud, and M. Acevedo. 1991
J.,
Hill, M.O. 1973. Diversity and evenness: a unifying no- Food habits of Great Horned Owl {Bubo virginianus)
tation and its consequences. Ecology 54:427—432. in the Cape Region of lower California, Mexico. J
Hoffmann, R.S. and D.L. Pattie. 1968. A guide to Mon- RaptorRes. 25:140-141.
MT
tana mammals. University Press, Missoula, U.S.A. Marti, C.D. 1974. Feeding ecology of four sympatric
Holt, D.W., E. Andrews, and N. Claflin. 1991. Non- owls. Condor 76:45-61.
breeding season diet of Northern Saw-whet Owls, Ae- 1976. Review of prey selection by Long-eared
.
golius acadicus, on Nantucket Island, Massachusetts. Owl. Condor 78:331-336.
Can. Field-Nat. 105:382-385. 1987. Raptor food habits studies. In B.A. Giron
.
. 1993. Trophic niche of nearctic Short-eared Pendleton, B.A. Millsap, K.W. Cline, and D.M. Bird
Owls. Wilson Bull. 105:497-503. [Eds.], Raptor management techniques manual. Nat
and S.M. Leasure. 1993. Short-eared Owl {Asia Wildl. Fed. Sci. & Tech. Ser. No. 10. Washington, DC
flammeus). InA. Poole and F. Gill [Eds.], The birds of U.S.A.
North America, No. 62. The Academy of Natural Sci- A
1989. long-term study of food-niche dynamics
.
ences, Philadelphia, PA and The American Ornithol- in the Common Barn Owl: comparisons within and
ogists’ Union, Washington, DC U.S.A.
between populations. Can.]. Zool. 66:1803-1812.
1994. Effects of Short-eared Owls on Common
. . 1992. Barn Owl {Tyto alba). In A. Poole, P. Stet-
Tern colony desertion, reproduction and mortality.
tenheim, and F. Gill [Eds.], The birds ofNorthAmer-
Colon. Waterbirds 17:1-6.
ica, No. 1, The Academy of Natural Sciences, Phila-
AND L.A. Leroux. 1996. Diets ofNorthern Pygmy-
delphia, PA and The American Ornithologists’
Owls and Northern Saw-whet Owls in west-central Union, Washington, DC U.S.A.
Montana. Wilson Bull. 108:123-128.
R. Berkley, C. Deppe, P.L. Enriquez-Rocha, P.D. . K. Steenhof, M.N. Kochert, and J.S. Marks
, 1993. Community trophic structure: the roles of diet,
Olsen, J.P. Petersen, J.L. Rangel-Salazar, and K.
body size, and activity time in vertebrate predators
Wood. 1999. Strigida species accounts. Pages 153-242
Oikos 67:6-18.
in], del Hoyo, A. Elliott, andj. Sargatal, [Eds.], Hand-
E. Korpimaki, and E.M. Jaksic. 1993. Trophic
book ofbirds of the world, Vol. 5. Lynx Edicions, Bar- ,
structure of raptor communities: a three-continent
celona, Spain.
and J.L. Petersen. 2000. Northern Pygmy-Owl comparison and synthesis. Ch. 2. /iiD.M. Power [Ed.],
Cxxrrent Ornithology, Vol. 10. Plenum, NYU.S.A.
{Glaucidium gnoma) In A. Poole and F. Gill [Eds.],
The birds of North. America, No. 494. The birds of and M.N. Kochert. 1996. Diet and trophic char-
North America, Inc., Philadelphia, PA U.S.A. acteristics ofGreat Horned Owls in southwestern Ida-
Houston, C.S., D.G. Smith, and C, Rohner. 1998. Great ho./. Field Ornithol. 67:499-506.
Horned Owl {Bubo virginianus) InA. Poole and E. Gill Maser, C. and E.D. Brodie,Jr. 1966. A study ofowl pellet
.
[Eds.], The birds of North America, No. 372. The contents from Linn, Benton, and Polk counties,
Birds ofNorth America, Inc., Philadelphia, PA U.S.A. Oregon. Murrelet 47:9-14.
Jaksic, F.M. and C.D. Marti. 1984. Comparative food , E.W. Hammer, and S.H. Anderson. 1970. Com-
habits of Bubo owls in Mediterranean-type ecosys- parative food habits of three owl species in central
tems. Condor 86:288-296. Oregon. Murrelet 51:29-33.
and M. Delibes, 1987. A comparative analysis of McInvaille, W.B. and L.B. Keith. 1974. Predator-preyre-
food niche relationships and trophic guild structure lations and breeding biology of the Great Horned
in two assemblages of vertebrate predators differing Owl and Red-tailed Hawk in central Alberta. Can
in species richness: causes, correlations and conse- Field-Nat. 88:1-20.
quences. Oecologia 71:461-472. Orians, G. and F. Kuhlman. 1956. Red-tailed Hawk and
1988. Trophic structure of some nearctic, neo- Great Horned Owl populations in Wisconsin. Condor
.
tropical and palearctic owl assemblages: potential 58:371-385.
roles of diet opportunism, interspecific interference Parmalee, D.F. 1992. Snowy Owl {Nyctea scandiaca). InA
and resource depression./. RaptorRes. 22:44—52. Poole and F. Gill [Eds.], The birds ofNorth America,
Kirkpatrick, C.M. and C.H. Conway. 1947. The winter No. 10. The Academy of Natural Sciences, Philadel-
foods of some Indiana owls. Am. Midi. Nat. 38:755- phia, PA and The American Ornithologists’ Union,
766. Washington, DC U.S.A.
Knight, R.L. and R.E. Jackman. 1984. Food niche rela- Proudfoot, G.A. 1997. Food habits of nesting Ferrugi-
tionships between Great Horned Owls and Common nous Pygmy Owls in southern Texas. Wilson Bull. 109.
Barn Owls in eastern Washington. Auk 101:175-179. 741-748.
Latham, R.M. 1950. The food of predaceous animals in Rickart, E.A. 1972. An analysis of Barn Owl and Great
March 2002 Great Horned Owl Trophic Niche 65
Horned Owl pellets from western Nebraska. Prairie Great Horned Owls in central Ohio. Ohio Sci. 78
J.
Nat. 4:35-38. 323-328.
Rohner, C. and F.I. Doyle. 1992. Food stressed Great Tyler,J.D. andJ.F.Jensen. 1981. Notes on foods ofGreat
Horned Owl kills adult Goshawk: exceptional obser- Horned Owls {Bubo virginianus) in Jackson County,
vation or community process? Raptor Res. 26:261- Oklahoma. Proc. Okla. Acad. Sci. 61:28-30.
J.
Voous, K.H. 1988. Owls of the northern hemisphere
263.
Rudolph, S. 1978. Predation ecology of coexisting Great MIT Press, Cambridge, MA U.S.A.
Horned and Barn owls. Wilson Bull. 90:134-137. Watson, A. 1957. The behavior, breeding and food ecol-
Rusch, D.H., E.C. Meslow, P.D. Doerr, and L.B. Keith. ogy of the Snowy Owl {Nyctea scandiaca). Ibis 99:419-
462.
1972. Response of Great Horned Owl populations to
Weir, D. and A. Hanson. 1989. Food habits of Great
changing prey densities./. Wildl. Manage. 36:282-296.
Horned Owls, Bubo virginianus, in the northern taiga
Seidensticker, J.C. 1968. Notes on the food habitats of ofthe Yukon Territory and Alaska. Can. Field-Nat. 103:
the Great Horned Owl in Montana. Murrelet
12-17.
Smith, D.G. andJ.R. Murphy. 1973. Breeding ecology of Whitaker, J.O, 1992. The Audubon Society field guide
raptors in the Eastern Great Basin of Utah. Brigham to North American mammals. Alfred A. Knopf, New
Young University. Science Bull. Biol. Series 18:1-76. NY
York, U.S.A.
Springer, M.A. and J.S. Kirkley. 1978. Inter- and intra-
specific interactions between Red-tailed Hawks and Received 27 October 2000; accepted 15 September 2001